To enable manifestation of plural functions by one part, and to aim at cost reduction by the reduction of number of parts and to plan miniaturization of car body by installing an air cleaner mechanism in a swing arm and by supplying an air being cleaned by an air cleaner mechanism to a carburetor of an engine.

In motorcycle 1 of motor scooter type, a swing arm 3a supports a rear-wheel 2 with a two-way arm at a free oscillation. By assembling an air cleaner mechanism in the left side swing arm 3a and by assembling a muffler mechanism in the right side swing arm, plural functions by one part are manifested. The swing arm 3a in which the air cleaner mechanism is installed is composed so that press-molded product of two pieces of right and left where it is formed from an intermediate swelling part of steel plate, and it is composed as a sandwiched structure by welding the peripheral part. In this way, not only a suspension function but also an air cleaner function and muffler function are obtained, and the cost reduction by the reduction of number of parts and the miniaturization of car body can be attained.